Pharmacology

The minimum inhibitory concentration for 90% of organisms for fidaxomicin against C. difficile is 0.9978 to 2 µg/mL.

Mechanism of action

Fidaxomicin is a bactericidal-type antibiotic that inhibits RNA polymerase sigma subunit. RNA polymerase is responsible for transcription in the bacteria therefore fidaxomicin will inhibit protein synthesis. As a result, apoptosis is triggered in susceptible organisms such as C. difficile.

Fidaxomicin is not systemically absorbed as shown by a plasma concentrations below the lower limit of quantification after single-dose or multiple-dose. In contrast, fecal concentrations of fidaxomicin are much higher and are concentration-dependent.
Cmax = 2 hours;
Tmax = 5.2 ng/mL;
AUC = 14 ng•hr/mL

Volume of distribution

Fidaxomicin is largely confined in the gastrointestinal tract and is not distributed extensively in the systemic.

Protein binding

Not Available

Metabolism

Fidaxomicin is hydrolyzed by gastric acid or intestinal microsomes into a less active metabolite (OP-1118). The cytochrome enzyme system are not involved in the metabolism of fidaxomicin.